Circuit for reducing interference



J y 1933' o. B. JACOBS 1,917,035 v CIRCUIT FOR REDUCING. INTERFERENCE Filed Feb. 25, 1932 2 Sheets-Sheet 1 PHASE 13 /2 507?. A g

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EHPF 2 m/vs/vrore I O. B. JACOBS A TTOR/VEY O. B. JACOBS CIRCUIT FOR-REDUCING INTERFERENCE Filed Feb. 25,

July 4, 1933.

1932 2 Sheets-Sheet 2 AMR DET.

INPUT if? PHA SE 50/? LPF EQR A SPEECH SPEECH ou TPUT INVENTOR O.B.JACOB$ BY ATTORNEY tion as the main cable, including a similar concentric sheath.

Signals received over the main cable pass from the core of the cable through two parallel paths. One path extends through the primary winding of transformer 4 and back through conductor 5 to the concentric return conductor of the main cable. The other path extends through the primary winding of transformer 6, sea-earth conductor 2 and balancing resistance 3 to the concentric return of the cable or cable sheath. Since the sea earth conductor 2 terminated by resistance 3 is designed to have the same impedance as the main cable, the total impedance offered to received signals in the path comprising transformer 6 is about twice as great as that inthe path comprising the primary of transformer 4 and connection 5 to the concentric return conductor.- The resistance noise impressed on the receiver through the input transformer 41's therefore only about onehalf that impressed through the transformer 6. The purpose of using the sea-earth conductor 2 is, as stated, to neutralizea large part of'thestaticinterference that is picked-up by the main cable. The conductor 2 is laid adjacent the main cable so that both conductors are subject to the same interference.

: The receiving conditions in the system as has been described are briefly as follows. Signals and interference from the main cable are received'by the primary of transformer 4. Signals accompanied by interference from the main cable and interference of the same character but Without signals from the conductor 2 are impressed upon the primary of transformer 6, with the result that the interference is reduced'and substantially eliminatedv while the signals are not materially reduced. The resistance noise received by transformer 4 is about half of the resistance" noise received by transformer 6 because of the similar reduction in the magnitude of the resistance component of the internal impedance of the cable circuit connected to the primary of transformer 4. Y

Currents from the respectivetransformers 4 and. 6-are transmitted through the individual amplifiers 7 and 8. The high-pass filter 9 confines the current in the output of amplifier 7 to the higher speech frequencies, comprising for example a range a few hundred cycles wide. Low-pass filter 10 confines the current in the output of amplifier 8 to a frequency range from the lower edge of the essential speech band, up to the cut-off; value =of the filter 9. The outputs from the amplifiers? and 8, as limited in frequency by the filters 9 and 10, are impressed in common on the input circuit of amplifier 11 Where they are furthered amplified and transmitted through the equalizer 12 to the receiving circuit'13 which may be of any suitable type such as a local receiver or a connection to a telephone exchange for repeating the received telephone current-s over other toll circuits or an ordinary subscribers line.

The equalizer 12 corrects at least partially for the unequal attentuation of the cable for the different speech frequencies and for this reason it introduces greater attenuation to the low frequencies in the speech range than to the high frequencies. The over-all gain of the receiving circuit is thus higher for the high speech frequencies than for the low. The use of the neutralizing sea-earth conductor 2, transformer 6 and transmission path 8, 10, results in the suppression of interference throughout the low frequency range where it is most troublesome. The use of the low internal resistance connection comprising conductor 1, transformer 4 and conductor 5 in connection with the transmission path 74), enables the higher frequency portions of the speech waves to be receivedwith only about half as much resistance noise as would be included if these high frequency components were received throughtransformer 6, that is, through the circuit comprising the sea-earth conductor 2 as a return.

, iunplifiers 7 and 8 may be omitted in this and subsequent figures. llf'they are used, they should have high impedance input circuits. If they are omitted,the filters 9 and 10 should have high input impedance out-- ".de their transmission frequency ranges and should not materially reduce the input im pe-dance of amplifier 11 which should be kept high in case: amplifiers 7 and 8 are not used. f

The concentric return shown in this and subsequent figures is not essential and may be omitted- That is, the distance represented by Y in. Fig.1 may be zero and conductor 5 may extend to the unction point of resistance 3: with. the cable sheath. Conversely, the two concentric shells around conductors 1 and 2 may be used and may extend all the way to the receiving set, in which case the distance X in Fig. 1 is zero. here the conducting sheaths around conductors 1 and 2 are used they are substantially in contact with each other. 3 e

In the circuit of Fig. 2 the low frequency interference currents are not balanced out in thetransforn'ier 6' as in the case of Fig. 1,

but are balanced out in the input circuit to amplifier 11. In this :case the entire speech band is transmitted through the path 'comprising transformer 4, amplifier 7, phase equalizerq14 and transformer to the input of amplifier 11. The other pathincludes lowpass filter 10 which confines transmission through this path to the lower frequencies 1 so that the amplified speech currents may be transmitted into the cable. These outgoing speech currents are applied between the cable core and the return conductor of the cable, or transmitting sea-earth. It is to be understood that the relay contacts may be arranged so that the short circuit on the transmitting path will not be released until the receiving paths are.short-circuited and that these remain short-circuitcd until the transmitting path is again short-circuited.

For a more complete disclosure of a voiceoperated s ritching system. adapted for use in connection with the present invention, in a two-way system of the general type indicated in Fig. 1, reference may be had to United States Patent No. 1,856,654, issued May 3, 1932, to C. N. Nebel.

It will be understood that the noise compensating arrangements illustrated in Figs. 1 and 3 are adapted for use in a twow-ay system equally as well. as the arrangement shown in Figs. 2 and a.

An advantage of the balancing arrange ments of Figs. 2 and 3 over that of Fig. 1 is that only one of the two receiving transformers need beconnected to the'cable core instead of both transformers asin Fig.1.

An advantage of the arrangement shown in Fig. 1 is that the gains of amplifiers 7 and 8, if used, may vary from each other without affectin the degree to which the .various types or noise are balanced out.

For simplicity of illustration, no shields have been shown for the transformers 4i and 6 of theh'rst three figures but it will be understood that shielding is to be assumed and may be like that of Fig. 4:.

Figs. 5 and 6 show how a more perfect balance can be obtained than Figs. 1 and 3, by use of a symmetrical circuit including a third transformer 30 and network 31. In Fig. 5, network 31 simulates the impedance looking to the left from the secondary of transformer t, so that conductors 1 and 2 are terminated symmetric-ally with respect to conductor 5. In Fig. 6 symmetry is obtained by making network 31 simulate the impedance into which transformer 6 works. These circuits permit a more complete neutralization of the interference currents.

Instead of effecting-all of the attenuation equalization in network 12, the amplifiers 7 and 8. can be given transmission characteristics such as to result n greaterampllfication at higher frequencles and thus produce an equalizing effect. It is not essential that equalizerfl2 be located at the point shown but it may be placed at any suitable point in the receiving circuit. The invention is capable of various changes and modifications within the scope of the appended claims.

What is claimed is:

1. In a receiving system, a main signaling conductor exposed to interference, an auxiliary conductor exposed to similar interference, a receiver, separate receiver coupling circuits for said conductors, one including said main conductor and auxiliary conductor in series whereby the interference energy recelved from both conductors is balanced out in the receiver, and the other circuit of lower resistance noise, said receiver connected to both of said coupling circuits, and filter means forimpressing only relatively high frequency currents from said circuit of lower resistance noise on said receiver whereby the resistance noise is kept low in the upper range of signal frequencies.

2. In a signal receiving system, a main sig naling conductor exposed to interference, an auxiliary circuit having transmission properties similar to those of the main conductor and exposed to similar interference, a receiver, means for applying to said receiver in- I terference energy from both conductors in.

opposed relation in the lower frequency portion of the signal range whereby the low frequency interference energy is balanced out but signals are received, and a circuit for impressing lower resistancenoise and signal energy of higher frequency range from said main conductor on said receiver where by the resistance noise is kept low in the region of high signal frequencies. i

3. A circult according to claim 2 inwhich phase ad ust1ng means is included between said receiver and said main conductor for changing the phase of the currents of certain other of said paths having a lower resistance noise level and-comprising a connection to the signaling conductor for applying higher l 3 Il asigr al receiving-System53 v r I {naling conductorexpqsed to interferefice, an j electricallysimiignailxilial yic on' I v lz u ly exposed to w interference,

' c eiver ia eir cuit c onnectin'gsaid receiver to; .v both conductorsin0pp0sec1shse whereby the 10v interference islbal zm'ced bubwhile the signals};

ynoise from said'receixferto said auxiliaity l frequency signal co'rinp'ohehtsto said re 'eiYer with-a lesseramountbf reslstanc'e "n ls than is present in the.first path.

a re fetained, a ,conn'eti'on iof low resistance conductor comprising; filter, ni'ea hs' fer im pressing resistzt ee noise of v high-frequencies only on said receiver, and ,ponnectlons 'be-ij' tween said receiver and saidfiCOnnectinggireuits whereby tliie resistsncefnoise e iergyvin said, connecting clr'e'ujits cqmblfie tea produce} "are du'cecl resultant resistanee'noise in there'- signal 'frequehcyfran'ge. Y

' pathskene such path cemprisirig'a eiic uit' -ineluding said 'tW conductors in se'riesfqrbaL ancing out the interferehee energy over only,

ceiver in, the hil'ier frequency portion i ofjgl f.

, 6. A two-Way signahng system comprising e amainsignaling-cgncluctor exposedlto int erfe'renee, an electrically similar auxiliarycon ductor similarly exposed tb interferene'e," a'reg V ceiving system conneete d "to 'receive Waves I from said condue'tofs oveff a fl-pliuiality of .the'lowfrequenc'yp'orti'on ofthe total signal range,lgn otherfoffl said p'aQthshaving: azlower resistance 'nbise levelandpomprisingspoil! ,J

11ec t1bnfwbhesignaling cenduet01 f0r applying ,h g ri-f tjequ'n y mfi lcol p n il i I 1' 1' J rl s r-a ouinw e i t-1 ane i qisethaniisfp resent in.- phe"1'irst path, a f v transmitting systemfasseciated with said're 'iceiving s stem and" 1c bn'hected" tpi jaid first mentioned path and ,YOiCe operzitedvswitehihg' means (5: 61 ".di sa-blingl" I connections b t een; v pgiths. and, said" ibeeeiving system re m tting system. 7. TA maingsignaling' c0pdue't0rrexpdsed' to lnt'erference,anauxiliaryeondlictor exposed to pra ctically identieal in terferei ee, ayl'ocz x ly Hearth conductor, a receiver; wpluralityi of .v coup lings between saidq receiver and said don- J upling circ liit'containing :a; j-

high ,frequency'"selectiveg circuit, and s'upp'ly I in'gsaid receiver Withva; peirtion "offthe signal 'frequeney j ran e 1 iI' 1". which interference is ,weaker than-themes istanceheise afiother of said-l c'diip'lings being: from-the gi iai i celidlictor -ar'i'cl i auxiliary COndutbr; and edritainifig f "-va gldw frequency selective circu-i'fl f ersiipply -j ing tosaid l 'eceiver a peiition of the -signal} "frequency range in hiehi the interference, c ui rents"arehighei'thantheresistance.ndise, 1 Q saicllatterficoupling"minimizing.vsaidjinter Y itnesswhereofil hereunbo siibseifibe 

